Rigs are used in wellbore operations such as drilling and servicing.
Tool carriers are employed in a rig to move one or more tools, and structures such as pipes and hoses, vertically relative to the mast. Tool carriers also pick up and manipulate the pipes and tools that are connected to form the wellbore string, such as a drill string, work string, liner, casing, etc.
In some embodiments, the tool carrier can be configured to hold any tool used in the drilling or servicing of wells, as is well known to those skilled in the art. A tool carrier can comprise a top drive or a power swivel. In the drilling of wells, a top drive unit can be used. In the servicing of wells, a power swivel or a top drive can be used. Top drives and power swivels can be similar in function and operation, the difference being that top drives can be larger in size and power, as may be required for the drilling of wells.
The tool carrier is installed in the mast on a drive assembly, which moves the tool carrier along the mast.
A tool carrier may be quite large and heavy. Generally, a tool carrier includes tool support structures for holding tools over well center and a back frame supporting the tool support structures and through which the tool carrier is connected to the drive assembly.
Slant rigs, which is a rig where the mast is oriented at an angle off vertical, present challenges to the operation of a tool carrier, as gravity cannot be employed to hold and center the tool support structures over well center.